Stacked modules and method

ABSTRACT

The present invention stacks integrated circuits into modules that conserve board surface area. In a precursor assembly devised as a component for a stacked circuit module in accordance with a preferred embodiment of the present invention, one or more stiffeners are disposed at least partially between a flex circuit and an integrated circuit. In a two-high stacked circuit module devised in accordance with a preferred embodiment of the present invention, an integrated circuit is stacked above a precursor assembly. The two integrated circuits are connected with the flex circuit of the precursor assembly. The present invention may be employed to advantage in numerous configurations and combinations of integrated circuits in modules.

RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 11/317,425 filed Dec. 22, 2005, which is a continuation of U.S.patent application Ser. No. 10/400,309 filed Mar. 27, 2003, which is acontinuation of U.S. patent application Ser. No. 10/005,581, filed Oct.26, 2001, now issued as U.S. Pat. No. 6,576,992 B2.

This application also is a continuation-in-part of U.S. patentapplication Ser. No. 11/258,438 filed Oct. 25, 2005, which is acontinuation-in-part of U.S. patent application Ser. No. 11/015,521,filed Dec. 17, 2004, pending, which is a continuation-in-part of U.S.patent application Ser. No. 10/845,029, filed May 13, 2004, pending,which is a continuation-in-part of PCT Application No. PCT/US03/29000,filed Sep. 15, 2003, pending.

This application also is a continuation-in-part of U.S. patentapplication Ser. No. 11/263,627, filed Oct. 31, 2005, pending, which isa continuation-in-part of U.S. patent application Ser. No. 10/958,584,filed Oct. 5, 2004, pending, which is a continuation of U.S. patentapplication Ser. No. 10/136,890, filed May 2, 2002, now U.S. Pat. No.6,940,729 B2, issued Sep. 6, 2005. U.S. patent application Ser. No.11/263,627 also is a continuation-in-part of U.S. patent applicationSer. No. 10/873,847, filed Jun. 22, 2004, pending, which is acontinuation of U.S. patent application Ser. No. 10/631,886, filed July11, 2003, pending, which is a continuation-in-part of U.S. patentapplication Ser. No. 10/453,398, filed Jun. 3, 2003, now U.S. Pat. No.6,914,324 B2, issued Jul. 5, 2005, which is a continuation-in-part ofU.S. patent application Ser. No. 10/005,581, filed Oct. 26, 2001, nowU.S. Pat. No. 6,576,992 B2, issued Jun. 10, 2003. U.S. patentapplication Ser. No. 10/631,886 also is a continuation-in-part of U.S.patent application Ser. No. 10/457,608, filed Jun. 9, 2003, pending,which is a continuation-in-part of U.S. patent application Ser. No.10/005,581, filed Oct. 26, 2001, now U.S. Pat. No. 6,576,992 B2, issuedJun. 10, 2003.

U.S. patent application Ser. Nos. 10/005,581, 10/136,890, 10/400,309,10/453,398, 10/457,608, 10/631,886, 10/845,029, 10/873,847, 10/958,584,11/015,521, 11/258,438, 11/263,627, 11/317,425, and PCT Application No.PCT/US03/29000 are hereby incorporated by reference for all purposes.

TECHNICAL FIELD

The present invention relates to aggregating integrated circuits and, inparticular, to stacking integrated circuits in chip-scale packages andmethods for creating stacked modules of chip-scale packages.

BACKGROUND

A variety of techniques are used to stack packaged integrated circuits.Some methods require special packages, while other techniques stackpackages configured to allow stand-alone deployment in an operatingenvironment.

“Chip scale packaging” or CSP refers generally to packages that provideconnection to an integrated circuit through a set of contacts (oftenembodied as “bumps” or “balls”) arrayed across a major surface of thepackage. Instead of leads emergent from a peripheral side of the packageas in “leaded” packages, in a CSP, contacts are placed on a majorsurface and typically emerge from the planar bottom surface of thepackage. The absence of “leads” on package sides renders most stackingtechniques devised for leaded packages inapplicable for CSP stacking.

CSP has enabled reductions in size and weight parameters for manyapplications. CSP is a broad category including a variety of packagesfrom near chip scale to die-sized packages such as the die sized ballgrid array (DSBGA). To meet the continuing demands for cost and formfactor reductions concurrent with increasing capabilities andcapacities, technologies that aggregate plural integrated circuit diesin a package been developed. The techniques and technology for stackingplural integrated circuit dies within a single package, however, are notgenerally applicable for stacking packages that are configured to allowstand-alone deployment in an operating environment.

There are several known techniques for stacking integrated circuitpackages articulated in chip scale technology. A variety of previoustechniques for stacking CSPs typically present complex structuralarrangements and thermal or high frequency performance issues. Forexample, thermal performance is a characteristic of importance in CSPstacks. With increasing operating frequencies of most systems, highfrequency performance issues are also increasingly important. Further,many stacking techniques result in modules that exhibit profiles tallerthan may be preferred for particular applications.

Staktek Group L.P., the assignee of the present invention, has developeda variety of stacked module designs that employ a form standard ormandrel that can provide thermal and/or construction advantages whileproviding a standard form that may allow use of a flexible circuitdesign with a variety of CSP types and body sizes. The mandrel or formstandard stack designs come in a variety of shapes and sizes andmaterials. Some form standards extend beyond the perimeter edge or theextent of the CSP body and thus provide a form about which the flexcircuitry transits. Some other form standards are substantially planarand have a lateral extent smaller than the lateral extent of an adjacentCSP. Although form standards provide numerous benefits in stacked moduledesigns, the use of form standards may add various cost and complexityissues to the design and manufacturing issues inherent with stackedmodules.

Stacked module design and assembly techniques and systems that provide athermally efficient, reliable structure that perform well at higherfrequencies but do not add excessive height to the stack that can bemanufactured at reasonable cost with readily understood and managedmaterials and methods are provided.

SUMMARY

The present invention allows chip scale-packaged integrated circuits(CSPs) that are configured to allow stand-alone deployment in anoperating environment to instead be stacked into modules that conservePWB or other board surface area. The present invention can be used toadvantage with CSP packages of a variety of sizes and configurationsranging from typical BGAs with footprints somewhat larger than thecontained die to smaller packages such as, for example, die-sizedpackages such as DSBGA. Although the present invention is applied mostfrequently to chip scale packages that contain one die, it may beemployed with chip scale packages that include more than one integratedcircuit die.

In a two-high CSP stack or module devised in accordance with a preferredembodiment of the present invention, two CSPs are stacked, with one CSPdisposed above the other. The two CSPs are connected with a pair of flexcircuits. Each of the pair of flex circuits is partially wrapped about arespective opposite lateral edge of the lower CSP of the module. Theflex circuit pair connects the upper and lower CSPs and provides athermal and electrical path connection path between the module and anapplication environment such as a printed wiring board (PWB).

In an alternate preferred embodiment of the present invention, aprecursor assembly for use as a component of a stacked circuit module isdevised having a CSP and a flex circuit with one or more stiffenersattached to the flex circuit. The stiffeners are disposed along a majorsurface of the CSP and may be attached to the major surface of the CSPby adhesive. Exemplary stacked circuit modules devised in accordancewith a preferred embodiment of the present invention comprise a secondCSP disposed above the CSP of the precursor assembly, the second CSPbeing connected to the upper portions of the flex circuit.

A tooling apparatus devised in accordance with a preferred embodiment ofthe present invention may be use to assemble precursor assemblies.Preferred embodiments of the tooling apparatus include a physical formused to impose a preselected distance between the edges of the flexcircuit, which in various embodiments comprises a flex aligner thatlimits the lateral placement of the edges of the flex circuit alongupper surface of the CSP.

The present invention may be employed to advantage in numerousconfigurations and combinations of CSPs in modules provided forhigh-density memories, high capacity computing, and other applications.

The present invention also provides methods for constructing stackedcircuit modules and precursor assemblies with flexible circuitry. Usingpreferred methods of the present invention, a single set of flexiblecircuitry, whether articulated as one or two flex circuits, may beemployed with CSP devices of a variety of configurations.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is an elevation view of module 10 devised in accordance with apreferred embodiment of the present invention.

FIG. 2 is an elevation view of module 10 devised in accordance with apreferred embodiment of the present invention.

FIG. 3 depicts, in enlarged view, the area marked “A” in FIG. 2.

FIG. 4 is an enlarged detail of an exemplar connection in a preferredembodiment of the present invention.

FIG. 5 is an enlarged depiction of an exemplar area around a lower flexcontact in a preferred embodiment of the present invention.

FIG. 6 depicts a first outer surface layer of a flex circuit employed ina preferred embodiment of the present invention.

FIG. 7 depicts a first outer surface layer of a flex circuit employed ina preferred embodiment of the present invention.

FIG. 8 depicts a first conductive layer of a flex circuit employed in apreferred embodiment of the present invention.

FIG. 9 illustrates a first conductive layer of a flex circuit employedin a preferred embodiment of the present invention.

FIG. 10 depicts an intermediate layer of a flex circuit employed in apreferred embodiment of the present invention.

FIG. 11 depicts an intermediate layer of a right side flex circuitemployed in a preferred embodiment of the present invention.

FIG. 12 depicts a second conductive layer of a flex circuit of apreferred embodiment of the present invention.

FIG. 13 depicts a second conductive layer of a flex circuit of apreferred embodiment of the present invention.

FIG. 14 depicts a second outer layer of a flex circuit employed in apreferred embodiment of the present invention.

FIG. 15 reflects a second outer layer of a flex circuit employed in apreferred embodiment of the present invention.

FIG. 16 depicts an alternative preferred embodiment of the presentinvention.

FIG. 17 illustrates a JEDEC pinout for DDR-II FBGA packages.

FIG. 18 illustrates the pinout of a module 10 in an alternativepreferred embodiment of the invention.

FIG. 19 illustrates the pinout of a module 10 in an alternativeembodiment of the invention.

FIG. 20 depicts the pinout of an exemplar CSP employed in a preferredembodiment of the invention.

FIG. 21 depicts a second conductive layer of a flex circuit employed inan alternative preferred embodiment of the present invention.

FIG. 22 depicts a second conductive layer of a flex circuit employed inan alternative preferred embodiment of the present invention.

FIG. 23 is an elevation view of a precursor assembly devised inaccordance with a preferred embodiment of the present inventioncomprising stiffeners.

FIG. 23A depicts, in enlarged view, the area marked “23A” in FIG. 23.

FIG. 24 is a plan view of stiffener stock devised in accordance with apreferred embodiment of the present invention.

FIG. 25 depicts, in enlarged view, the area marked “25” in FIG. 24.

FIG. 26 is a perspective view of a panel or strip comprising flexcircuits devised in accordance with a preferred embodiment of thepresent invention with stiffener stock attached.

FIG. 27 is a plan view of a panel or strip comprising flex circuitsdevised in accordance with a preferred embodiment of the presentinvention with stiffener stock attached.

FIG. 28 depicts, in enlarged view, the area marked “28” in FIG. 24.

FIG. 29 depicts a CSP placed on a flex circuit in accordance with apreferred embodiment of the present invention.

FIG. 30 presents another depiction of a CSP placed on a flex circuit inaccordance with a preferred embodiment of the present invention.

FIG. 31 depicts two flex circuit edges in an arrangement according to apreferred embodiment of the present invention.

FIG. 32 depicts two flex edges in accordance with an alternativepreferred embodiment of the present invention.

FIG. 33 is a plan view from below of a precursor assembly devised inaccordance with a preferred embodiment of the present invention.

FIG. 34 is an elevation view of a stacked circuit module devised inaccordance with a preferred embodiment of the present invention.

FIG. 35 is an elevation view of a stacked circuit module devised inaccordance with another preferred embodiment of the present invention.

FIG. 36 is a perspective view from below of a stacked circuit moduledevised in accordance with a preferred embodiment of the presentinvention.

FIG. 37 is a perspective view from above of a stacked circuit moduledevised in accordance with a preferred embodiment of the presentinvention.

FIG. 38 is an elevation view of a stacked circuit module devised inaccordance with another preferred embodiment of the present invention.

FIG. 39 depicts a tooling apparatus devised in accordance with apreferred embodiment of the present invention.

FIG. 40 depicts an enlarged depiction of the area marked “40” in FIG.39.

FIG. 41 illustrates a tooling apparatus in accordance with a preferredembodiment of the present invention.

FIG. 42 illustrates another step in devising an assembly in accordancewith a preferred embodiment of the present invention.

FIG. 43 depicts another step in devising an assembly in accordance witha preferred embodiment of the present invention.

FIG. 44 depicts a tooling apparatus devised in accordance with anotherpreferred embodiment of the present invention, and illustrates a step inaccordance with another preferred embodiment of the present invention.

FIG. 45 illustrates another step in devising an assembly in accordancewith another preferred embodiment of the present invention.

FIG. 46 depicts another step in devising an assembly in accordance withanother preferred embodiment of the present invention.

FIG. 47 illustrates another step in devising an assembly in accordancewith another preferred embodiment of the present invention.

FIG. 48 depicts another step in devising an assembly in accordance withanother preferred embodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 is an elevation view of module 10 devised in accordance with apreferred embodiment of the present invention. Module 10 is comprised ofupper CSP 12 and lower CSP 14. Each of CSPs 12 and 14 have an uppersurface 16 and a lower surface 18 and opposite lateral sides 20 and 22.

The invention is used with CSP packages of a variety of types andconfigurations such as, for example, those that are die-sized, as wellthose that are near chip-scale as well as the variety of ball grid arraypackages known in the art. Collectively, these will be known herein aschip scale packaged integrated circuits (CSPs) and preferred embodimentswill be described in terms of CSPs, but the particular configurationsused in the explanatory figures are not, however, to be construed aslimiting. For example, the elevation views of FIGS. 1 and 2 are depictedwith CSPs of a particular profile known to those in the art, but itshould be understood that the figures are exemplary only. Later figuresshow embodiments of the invention that employ CSPs of otherconfigurations as an example of one other of the many alternative CSPconfigurations with which the invention may be employed. The inventionmay be employed to advantage in the wide range of CSP configurationsavailable in the art where an array of connective elements is availablefrom at least one major surface. The invention is advantageouslyemployed with CSPs that contain memory circuits but may be employed toadvantage with logic, computing, and other types of circuits where addedcapacity without commensurate PWB or other board surface areaconsumption is desired.

Typical CSPs, such as, for example, ball-grid-array (“BGA”),micro-ball-grid array (“μBGA”), and fine-pitch ball grid array (“FBGA”)packages have an array of connective contacts embodied, f6r example, asleads, bumps, solder balls, or balls that extend from lower surface 18of a plastic casing in any of several patterns and pitches. An externalportion of the connective contacts is often finished with a ball ofsolder. Shown in FIG. 1 are CSP contacts 24 along lower surfaces 18 ofCSPs 12 and 14. CSP contacts 24 provide connection to the integratedcircuit within the respective packages. Collectively, CSP contacts 24comprise CSP array 26 shown as to lower CSP 14 in the depictedparticular package configuration as CSP arrays 26 ₁ and 26 ₂ whichcollectively comprise CSP array 26.

In FIG. 1, flex circuits (“flex”, “flex circuits” or “flexible circuitstructures”) 30 and 32 are shown partially wrapped about lower CSP 14with flex 30 partially wrapped over lateral side 20 of lower CSP 14 andflex 32 partially wrapped about lateral side 22 of lower CSP 14. Lateralsides 20 and 22 may be in the character of sides or may, if the CSP isespecially thin, be in the character of an edge. Any flexible orconformable substrate with a multiple internal layer connectivitycapability may be used as a flex circuit in the invention. The entireflex circuit may be flexible or, as those of skill in the art willrecognize, a PCB structure made flexible in certain areas to allowconformability around lower CSP 14 and rigid in other areas forplanarity along CSP surfaces may be employed as an alternative flexcircuit in the present invention. For example, structures known asrigid-flex may be employed.

Portions of flex circuits 30 and 32 are fixed to upper surface 16 oflower CSP 14 by adhesive 34 which is shown as a tape adhesive, but maybe a liquid adhesive or may be placed in discrete locations across thepackage. Preferably, adhesive 34 is thermally conductive. Adhesives thatinclude a flux are used to advantage in assembly of module 10. Layer 34may also be a thermally conductive medium to encourage heat flow betweenthe CSPs of module 10.

Flex circuits 30 and 32 are multi-layer flexible circuit structures thathave at least two conductive layers. Preferably, the conductive layersare metal such as alloy 110. The use of plural conductive layersprovides advantages as will be seen and the creation of a distributedcapacitance across module 10 intended to reduce noise or bounce effectsthat can, particularly at higher frequencies, degrade signal integrity,as those of skill in the art will recognize. Module 10 of FIG. 1 hasmodule contacts 36 collectively identified as module array 38.

FIG. 2 shows a module 10 devised in accordance with a preferredembodiment of the invention. FIG. 2 illustrates use of a conformal media40 provided in a preferred embodiment to assist in creating conformalityof structural areas of module 10. Planarity of the module is improved byconformal media 40. Preferably, conformal media 40 is thermallyconductive. In alternative embodiments, thermal spreaders or a thermalmedium may be placed as shown by reference 41. Identified in FIG. 2 areupper flex contacts 42 and lower flex contacts 44 that are at one of theconductive layers of flex circuits 30 and 32. Upper flex contacts 42 andlower flex contacts 44 are conductive material and, preferably, aresolid metal. Lower flex contacts 44 are collectively lower flex contactarray 46. Upper flex contacts 42 are collectively upper flex contactarray 48. Only some of upper flex contacts 42 and lower flex contacts 44are identified in FIG. 2 to preserve clarity of the view. It should beunderstood that each of flex circuits 30 and 32 have both upper flexcontacts 42 and lower flex contacts 44. Lower flex contacts 44 areemployed with lower CSP 14 and upper flex contacts 42 are employed withupper CSP 12. FIG. 2 has an area marked “A” that is subsequently shownin enlarged depiction in FIG. 3.

FIG. 3 depicts in enlarged view, the area marked “A” in FIG. 2. FIG. 3illustrates the connection between example CSP contact 24 and modulecontact 36 through lower flex contact 44 to illustrate the solid metalpath from lower CSP 14 to module contact 36 and, therefore, to anapplication PWB to which module is connectable. As those of skill in theart will understand, heat transference from module 10 is therebyencouraged.

With continuing reference to FIG. 3, CSP contact 24 and module contact36 together offset module 10 from an application platform such as a PWB.The combined heights of CSP contact 24 and module contact 36 provide amoment arm longer than the height of a single CSP contact 24 alone. Thisprovides a longer moment arm through whichtemperature-gradient-over-time stresses (such as typified by tempcycle), can be distributed.

Flex 30 is shown in FIG. 3 to be comprised of multiple layers. Flex 30has a first outer surface 50 and a second outer surface 52. Flex circuit30 has at least two conductive layers interior to first and second outersurfaces 50 and 52. There may be more than two conductive layers in flex30 and flex 32. In the depicted preferred embodiment, first conductivelayer 54 and second conductive layer 58 are interior to first and secondouter surfaces 50 and 52. Intermediate layer 56 lies between firstconductive layer 54 and second conductive layer 58. There may be morethan one intermediate layer, but one intermediate layer of polyimide ispreferred.

As depicted in FIG. 3 and seen in more detail in later figures, lowerflex contact 44 is preferably comprised from metal at the level ofsecond conductive layer 58 interior to second outer surface 52. Lowerflex contact 44 is solid metal in a preferred embodiment and iscomprised of metal alloy such as alloy 110. This results in a solidmetal pathway from lower CSP 14 to an application board therebyproviding a significant thermal pathway for dissipation of heatgenerated in module 10.

FIG. 4 is an enlarged detail of an exemplar connection between exampleCSP contact 24 and example module contact 36 through lower flex contact44 to illustrate the solid metal path from lower CSP 14 to modulecontact 36 and, therefore, to an application PWB to which module 10 isconnectable. As shown in FIG. 4, lower flex contact 44 is at secondconductive layer 58 that is interior to first and second outer surfacelayers 50 and 52 respectively, of flex circuit 30.

FIG. 5 is an enlarged depiction of an exemplar area around a lower flexcontact 44 in a preferred embodiment. Windows 60 and 62 are opened infirst and second outer surface layers 50 and 52 respectively, to provideaccess to particular lower flex contacts 44 residing at the level ofsecond conductive layer 58 in the flex. The upper flex contacts 42 arecontacted by CSP contacts 24 of upper CSP 12. Lower flex contacts 44 andupper flex contacts 42 are particular areas of conductive material(preferably metal such as alloy 110) at the level of second conductivelayer 58 in the flex. Upper flex contacts 42 and lower flex contacts 44are demarked in second conductive layer 58 and, as will be shown insubsequent Figs., may be connected to or isolated from the conductiveplane of second conductive layer 58. Demarking a lower flex contact 44from second conductive layer 58 is represented in FIG. 5 by demarcationgap 63 shown at second conductive layer 58. Where an upper or lower flexcontact 42 or 44 is not completely isolated from second conductive layer58, demarcation gaps do not extend completely around the flex contact asshown, for example, by lower flex contacts 44C in later FIG. 12. CSPcontacts 24 of lower CSP 14 pass through a window 60 opened throughfirst outer surface layer 50, first conductive layer 54, andintermediate layer 56, to contact an appropriate lower flex contact 44.Window 62 is opened through second outer surface layer 52 through whichmodule contacts 36 pass to contact the appropriate lower flex contact44.

Respective ones of CSP contacts 24 of upper CSP 12 and lower CSP 14 areconnected at the second conductive layer 58 level in flex circuits 30and 32 to interconnect appropriate signal and voltage contacts of thetwo CSPs. Respective CSP contacts 24 of upper CSP 12 and lower CSP 14that convey ground (VSS) signals are connected at the first conductivelayer 54 level in flex circuits 30 and 32 by vias that pass throughintermediate layer 56 to connect the levels as will subsequently bedescribed in further detail. Thereby, CSPs 12 and 14 are connected.Consequently, when flex circuits 30 and 32 are in place about lower CSP14, respective CSP contacts 24 of each of upper and lower CSPs 12 and 14are in contact with upper and lower flex contacts 42 and 44,respectively. Selected ones of upper flex contacts 42 and lower flexcontacts 44 are connected. Consequently, by being in contact with lowerflex contacts 44, module contacts 36 are in contact with both upper andlower CSPs 12 and 14.

In a preferred embodiment, module contacts 36 pass through windows 62opened in second outer layer 52 to contact lower flex contacts 44. Insome embodiments, as will be later shown, module 10 will exhibit amodule contact array 38 that has a greater number of contacts than dothe constituent CSPs of module 10. In such embodiments, some of modulecontacts 36 may contact lower flex contacts 44 that do not contact oneof the CSP contacts 24 of lower CSP 14 but are connected to CSP contacts24 of upper CSP 12. This allows module 10 to express a wider datapaththan that expressed by the constituent CSPs 12 or 14. A module contact36 may also be in contact with a lower flex contact 44 to provide alocation through which different levels of CSPs in the module may beenabled when no unused CSP contacts are available or convenient for thatpurpose.

In a preferred embodiment, first conductive layer 54 is employed as aground plane, while second conductive layer 58 provides the functions ofbeing a signal conduction layer and a voltage conduction layer. Those ofskill will note that roles of the first and second conductive layers maybe reversed with attendant changes in windowing and use of commensurateinterconnections.

As those of skill will recognize, interconnection of respective voltageCSP contacts 24 of upper and lower CSPs 12 and 14 will provide a thermalpath between upper and lower CSPs to assist in moderation of thermalgradients through module 10. Such flattening of the thermal gradientcurve across module 10 is further encouraged by connection of commonground CSP contacts 24 of upper and lower CSPs 12 and 14 through firstconductive layer 54. Those of skill will notice that between first andsecond conductive layers 54 and 58 there is at least one intermediatelayer 56 that, in a preferred embodiment, is a polyimide. Placement ofsuch an intermediate layer between ground-conductive first conductivelayer 54 and signal/voltage conductive second conductive layer 58provides, in the combination, a distributed capacitance that assists inmitigation of ground bounce phenomena to improve high frequencyperformance of module 10.

In a preferred embodiment, FIG. 6 depicts first outer surface layer 50of flex 30 (i.e., left side of FIG. 1). The view is from above the flexlooking down into flex 30 from the perspective of first conductive layer54. Throughout the Figs., the location reference “B” is to orient viewsof layers of flex 30 to those of flex 32 as well as across layers.Windows 60 are opened through first outer surface layer 50, firstconductive layer 54, and intermediate layer 56. CSP contacts 24 of lowerCSP 14 pass through windows 60 of first outer surface layer 50, firstconductive layer 54, and intermediate layer 56 to reach the level ofsecond conductive layer 58 of flex 30. At second conductive layer 58,selected CSP contacts 24 of lower CSP 14 make contact with selectedlower flex contacts 44. Lower flex contacts 44 provide several types ofconnection in a preferred embodiment as will be explained with referenceto later FIG. 12. When module 10 is assembled, a portion of flex 30 willbe wrapped about lateral side 20 of lower CSP 14 to place edge 62 aboveupper surface 16 of lower CSP 14.

In a preferred embodiment, FIG. 7 depicts first outer surface layer 50of flex 32 (i.e., right side of FIG. 1). The view is from above the flexlooking down into flex 32 from the perspective of first conductive layer54. The location reference “B” relatively orients the views of FIGS. 6and 7. The views of FIGS. 6 and 7 may be understood together with thereference marks “B” of each view being placed nearer each other than toany other corner of the other view of the pair of views of the samelayer. As shown in FIG. 7, windows 60 are opened through first outersurface layer 50, first conductive layer 54 and intermediate layer 56.CSP contacts 24 of lower CSP 14 pass through windows 60 of first outersurface layer 50, first conductive layer 54, and intermediate layer 56to reach the level of second conductive layer 58 of flex 30. At secondconductive layer 58, selected CSP contacts 24 of lower CSP 14 makecontact with lower flex contacts 44. Lower flex contacts 44 provideseveral types of connection in a preferred embodiment as will beexplained with reference to later FIG. 12. When module 10 is assembled,a portion of flex 32 will be wrapped about lateral side 22 of lower CSP14 to place edge 64 above upper surface 16 of lower CSP 14.

FIG. 8 depicts first conductive layer 54 of flex 30. Windows 60 continuethe opened orifice in flex 30 through which CSP contacts 24 of lower CSP14 pass to reach second conductive layer 58 and, therefore, selectedlower flex contacts 44 at the level of second conductive layer 58.

Those of skill will recognize that as flex 30 is partially wrapped aboutlateral side 20 of lower CSP 14, first conductive layer 54 becomes, onthe part of flex 30 disposed above upper surface 16 of lower CSP 14, thelower-most conductive layer of flex 30 from the perspective of upper CSP12. In the depicted embodiment, those CSP contacts 24 of upper CSP 12that provide ground (VSS) connections are connected to the firstconductive layer 54. First conductive layer 54 lies beneath, however,second conductive layer 58 in that part of flex 30 that is wrapped abovelower CSP 14. Consequently, some means must be provided for connectionof the upper flex contact 42 to which ground-conveying CSP contacts 24of upper CSP 12 are connected and first conductive layer 54.Consequently, in the depicted preferred embodiment, those upper flexcontacts 42 that are in contact with ground-conveying CSP contacts 24 ofupper CSP 12 have vias that route through intermediate layer 56 to reachfirst conductive layer 54. The sites where those vias meet firstconductive layer 54 are identified in FIG. 8 as vias 66. These vias maybe “on-pad” or coincident with the flex contact 42 to which they areconnected. Those of skill will note a match between the vias 66identified in FIG. 8 and vias 66 identified in the later view of secondconductive layer 58 of the depicted preferred embodiment. In a preferredembodiment, vias 66 in coincident locations from Fig. to Fig. are onevia. For clarity of the view, depicted vias in the figures are shownlarger in diameter than in manufactured embodiments. As those of skillwill recognize, the connection between conductive layers provided byvias (on or off pad) may be provided any of several well-knowntechniques such as plated holes or solid lines or wires and need notliterally be vias.

Also shown in FIG. 8 are off-pad vias 74. Off-pad vias 74 are disposedon first conductive layer 54 at locations near, but not coincident withselected ones of windows 60. Unlike vias 66 that connect selected onesof upper flex contacts 42 to first conductive layer 54, off-pad vias 74connect selected ones of lower flex contacts 44 to first conductivelayer 54. In the vicinity of upper flex contacts 42, second conductivelayer 58 is between the CSP connected to module 10 by the upper flexcontacts 42 (i.e., upper CSP 12) and first conductive layer 54.Consequently, vias between ground-conveying upper flex contacts 42 andfirst conductive layer 54 may be directly attached to the selected upperflex contacts 42 through which ground signals are conveyed. In contrast,in the vicinity of lower flex contacts 44, first conductive layer 54 isbetween the CSP connected to module 10 by the lower flex contacts 44(i.e., lower CSP 14) and second conductive layer 58. Consequently, viasbetween ground-conveying lower flex contacts 44 and first conductivelayer 54 are offset from the selected lower flex contacts 44 by off-padvias 74 shown in offset locations.

FIG. 9 illustrates first conductive layer 54 of flex 32. The locationreference marks “B” are employed to relatively orient FIGS. 8 and 9.Windows 60, vias 66 and off-pad vias 74 are identified in FIG. 9. Alsoshown in FIG. 9, are enable vias 68 and 70 and enable trace 72. Enablevia 70 is connected off-pad to a selected lower flex contact 44 thatcorresponds, in this preferred embodiment, to an unused CSP contact 24of lower CSP 14 (i.e., a N/C). A module contact 36 at that site conveysan enable signal (C/S) for upper CSP 12 through the selected lower flexcontact 44 (which is at the level of second conductive layer 58) tooff-pad enable via 70 that conveys the enable signal to first conductivelayer 54 and thereby to enable trace 72. Enable trace 72 further conveysthe enable signal to enable via 68 which extends through intermediatelayer 56 to selected upper flex contact 42 at the level of secondconductive layer 58 where contact is made with the C/S pin of upper CSP12. Thus, upper and lower CSPs 12 and 14 may be independently enabled.

FIG. 10 depicts intermediate layer 56 of flex 30. Windows 60 are shownopened in intermediate surface 56. CSP contacts 24 of lower CSP 14 passthrough windows 60 in intermediate layer 58 to reach lower flex contacts44 at the level of second conductive layer 58. Those of skill willnotice that, in the depicted preferred embodiment, windows 60 narrow indiameter from their manifestation in first outer layer 50. Vias 66,off-pad vias 74, and enable vias 68 and 70 pass through intermediatelayer 56 connecting selected conductive areas at the level of first andsecond conductive layers 54 and 58, respectively. FIG. 11 depictsintermediate layer 56 of flex 32 showing windows 60, vias 66, off-padvias 74, and enable vias 68 and 70 passing through intermediate layer56.

FIG. 12 depicts second conductive layer 58 of flex 30 of a preferredembodiment of the present invention. Depicted are various types of upperflex contacts 42, various types of lower flex contacts 44, signal traces76, and VDD plane 78 as well as previously described vias 66 and off-padvias 74. Throughout FIGS. 12 and 13, only exemplars of particularfeatures are identified to preserve clarity of the view. Flex contacts44A are connected to corresponding selected upper flex contacts 42A withsignal traces 76. To enhance the clarity of the view, only exemplarindividual flex contacts 44A and 42A are literally identified in FIG.12. As shown, in this preferred embodiment, signal traces 76 exhibitpath routes determined to provide substantially equal signal lengthsbetween corresponding flex contacts 42A and 44A. As shown, traces 76 areseparated from the larger surface area of second conductive layer 58that is identified as VDD plane 78. VDD plane 78 may be in one or moredelineated sections but, preferably is one section. Lower flex contacts44C provide connection to VDD plane 78. In a preferred embodiment, upperflex contacts 42C and lower flex contacts 44C connect upper CSP 12 andlower CSP 14, respectively, to VDD plane 78. Lower flex contacts 44 thatare connected to first conductive layer 54 by off-pad vias 74 areidentified as lower flex contacts 44B. To enhance the clarity of theview, only exemplar individual lower flex contacts 44B are literallyidentified in FIG. 12. Upper flex contacts 42 that are connected tofirst conductive layer 54 by vias 66 are identified as upper flexcontacts 42B.

FIG. 13 depicts second conductive layer 58 of right side flex 32 of apreferred embodiment of the present invention. Depicted are varioustypes of upper flex contacts 42, various types of lower flex contacts44, signal traces 76, and VDD plane 78 as well as previously describedvias 66, off-pad vias 74, and enable vias 70 and 68. FIG. 13 illustratesupper flex contacts 42A connected by traces 76 to lower flex contacts44A. VDD plane 78 provides a voltage plane at the level of secondconductive layer 58. Lower flex contacts 44C and upper flex contacts 42Cconnect lower CSP 14 and upper CSP 12, respectively, to VDD plane 78.Lower flex contact 44D is shown with enable via 70 described earlier.Corresponding upper flex contact 42D is connected to lower flex contact44D through enable vias 70 and 68 that are connected to each otherthrough earlier described enable trace 72 at the first conductive layer54 level of flex 32.

FIG. 14 depicts second outer layer 52 of flex 30. Windows 62 areidentified. Those of skill will recognize that module contacts 36 passthrough windows 62 to contact appropriate lower flex contacts 44. Whenflex 30 is partially wrapped about lateral side 20 of lower CSP 14, aportion of second outer layer 52 becomes the upper-most layer of flex 30from the perspective of upper CSP 12. CSP contacts 24 of upper CSP 12pass through windows 64 to reach second conductive layer 58 and makecontact with appropriate ones of upper flex contacts 42 located at thatlevel. FIG. 15 reflects second outer layer 52 of flex 32 and exhibitswindows 64 and 62. Module contacts 36 pass through windows 62 to contactappropriate lower flex contacts 44. CSP contacts 24 of upper CSP 12 passthrough windows 64 to reach second conductive layer 58 and make contactwith appropriate ones of upper flex contacts 42 located at that level.

FIG. 16 depicts an alternative preferred embodiment of the presentinvention showing module 10. Those of skill will recognize that theembodiment depicted in FIG. 16 differs from that in FIG. 2 by thepresence of module contacts 36E. Module contacts 36E supply a part ofthe datapath of module 10 and may provide a facility for differentialenablement of the constituent CSPs. A module contact 36E not employed inwide datapath provision may provide a contact point to supply an enablesignal to differentially enable upper CSP 12 or lower CSP 14.

In a wide datapath module 10, the data paths of the constituent upperCSP 12 and lower CSP 14 are combined to provide a module 10 thatexpresses a module datapath that is twice the width of the datapaths ofthe constituent CSPs in a two-high module 10. The preferred method ofcombination is concatenation, but other combinations may be employed tocombine the datapaths of CSPs 12 and 14 on the array of module contacts36 and 36E.

As an example, FIGS. 17, 18, and 19 are provided to illustrate usingadded module contacts 36E in alternative embodiments of the presentinvention to provide wider datapaths for module 10 than are present inconstituent CSPs 12 and 14. FIG. 17 illustrates a JEDEC pinout forDDR-II FBGA packages. FIG. 18 illustrates the pinout provided by modulecontacts 36 and 36E of a module 10 expressing an 8-bit wide datapath.Module 10 is devised in accordance with the present invention and is, inthe exemplar embodiment, comprised of an upper CSP 12 and lower CSP 14that are DDR-II-compliant in timing, but each of which are only 4 bitswide in datapath. As will be recognized, the module 10 mapped in FIG. 18expresses an 8-bit wide datapath. For example, FIG. 18 depicts DQ pinsdifferentiated in source between upper CSP 12 (“top”) and lower CSP 14(“bot”) to aggregate to 8-bits. FIG. 19 illustrates the pinout providedby module contacts 36 and 36E of module 10 expressing a 16-bit widedatapath. Module 10 is devised in accordance with the present inventionand is, in this exemplar embodiment, comprised of an upper CSP 12 andlower CSP 14 that are DDR-II-compliant in timing, but each of which areonly 8-bits wide in datapath. Those of skill in the art will recognizethat the wide datapath embodiment may be employed with any of a varietyof CSPs available in the field and such CSPs need not be DDR compliant.

FIG. 20 illustrates a typical pinout of a memory circuit provided as aCSP and useable in the present invention. Individual array positions areidentified by the JEDEC convention of numbered columns and alphabeticrows. The central area (e.g., A3-A6; B3-B6; etc.) is unpopulated. CSPcontacts 24 are present at the locations that are identified byalpha-numeric identifiers such as, for example, A3, shown as an exampleCSP contact 24. FIG. 21 depicts second metal layer 58 of flex 30 in analternative embodiment of the invention in which module 10 expresses adatapath wider than that expressed by either of the constituent CSPs 12and 14. Lower flex contacts 44E are not contacted by CSP contacts 24 oflower CSP 14, but are contacted by module contacts 36E to provide, withselected module contacts 36, a datapath for module 10 that is 2n-bits inwidth where the datapaths of CSPs 12 and 14 have a width of n-bits. Asshown in FIG. 21, lower flex contacts 44E are connected to upper flexcontacts 42E. As shown in earlier FIG. 14, windows 62 pass throughsecond outer layer 52. In the alternative preferred embodiment for whichsecond conductive layer 58 is shown in FIG. 21, module contacts 36 and36E pass through windows 62 in second outer layer 52 of flex circuit 30,to contact appropriate lower flex contacts 44.

FIG. 22 illustrates second metal layer 58 of flex 32 in an alternativeembodiment of the invention in which module 10 expresses a datapathwider than that expressed by either of the constituent CSPs 12 and 14.Lower flex contacts 44E are not contacted by CSP contacts 24 of lowerCSP 14, but are contacted by module contacts 36E to provide, withselected module contacts 36, a datapath for module 10 that is 2n-bits inwidth where the datapaths of CSPs 12 and 14 have a width of n-bits. Asshown in FIG. 22, lower flex contacts 44E are connected to upper flexcontacts 42E. As shown in earlier FIG. 14, windows 62 pass throughsecond outer layer 52. In the alternative preferred embodiment for whichsecond conductive layer 58 is shown in FIG. 22, module contacts 36 passthrough windows 62 in second outer layer 52 of flex circuit 32, tocontact appropriate lower flex contacts 44.

In particular, in the embodiment depicted in FIGS. 21 and 22, modulecontacts 36E contact flex contacts 44E and 44EE. Those of skill willrecognize that lower flex contacts 44E are, in the depicted embodiment,eight (8) in number and that there is another lower flex contactsidentified by reference 44EE shown on FIG. 21. Lower flex contact 44EEis contacted by one of the module contacts 36E to provide differentialenablement between upper and lower CSPs. Those of skill will recognizethat lower flex contacts 44E are connected to corresponding upper flexcontacts 42E. CSP contacts 24 of upper CSP 12 that convey data are incontact with upper flex contacts 42E. Consequently, the datapaths ofboth upper CSP 12 and lower CSP 14 are combined to provide a widedatapath on module 10. With the depicted connections of FIGS. 21 and 22,lower flex contacts 44E of flex circuits 30 and 32 convey to modulecontacts 36E, the datapath of upper CSP 12, while other lower flexcontacts 44 convey the datapath of lower CSP 14 to module contacts 36 toprovide module 10 with a module datapath that is the combination of thedatapath of upper CSP 12 and lower CSP 14. In the depicted particularembodiment of FIGS. 21 and 22, module 10 expresses a 16-bit datapath andCSP 12 and CSP 14 each express an 8-bit datapath.

FIGS. 23-33 depict aspects of alternative preferred embodiments of aprecursor assembly for use as a component of a stacked circuit module.FIGS. 23-33 depict aspects of stiffeners comprised in exemplaryprecursor assemblies and additional aspects of other components used inmanufacturing such precursor assemblies. FIG. 23 is an elevation view ofan end of precursor assembly 105 comprising CSP 114 having an uppersurface 116, a lower surface 118, and opposite lateral sides 120 and122. Upon assembly of a stacked circuit module 110 using precursorassembly 105 of this embodiment, CSP 114 will become a lower CSP of astacked circuit module 110.

Among the various CSPs that are useful for CSP 114 are the types thatinclude at least one integrated circuit or semiconductor chip surroundedby a package body 127 with a lateral extent L defined by the oppositelateral edges or sides 120 and 122. The package body surrounding theintegrated circuit(s) or semiconductor chip(s) need not be plastic, buta large majority of package bodies in CSP technologies are plastic. Thepackage body need not surround the integrated circuit(s) orsemiconductor chip(s) completely, leaving one or more sides, edges,surfaces, or other regions of the integrated circuit(s) or semiconductorchip(s) exposed, but a large majority of package bodies in CSPtechnologies completely encase the integrated circuit(s) orsemiconductor chip(s) or leave only the terminals on integrated circuitor semiconductor chip active face(s) exposed. The invention may also beused with those CSP-like packages that exhibit bare die connectives onone major surface.

Those of skill will realize that various embodiments of the presentinvention may be devised to create modules and precursor assemblies withdifferent size CSPs and that the constituent CSPs may be of differenttypes within the same stacked circuit module 110. The disclosedstructures and methods allow a single set of flex circuitry, whethercomprised of one or two flex circuits, to be employed with a variety ofpackage body sizes of CSPs. For example, one of the constituent CSPs ofan example stacked circuit module 110 may be a typical CSP havinglateral edges 120 and 122 that have an appreciable height to present a“side” while other constituent CSPs of the same stacked circuit module110 may be devised in packages that have lateral edges 120 and 122 thatare more in the character of an edge rather than a side havingappreciable height. All devices such as those discussed above andsimilar devices are included within the meaning of the term CSP, whichterm should be broadly considered in the context of this application.

The embodiment of a precursor assembly illustrated in FIG. 23 usessubstantially planar stiffeners 139 that are initially disposed on aflex circuit 130 and affixed thereto with adhesive 134. When precursorassembly 105 is assembled, stiffeners 139 are disposed along a surfaceof CSP 114 even if literally separated from that surface, such as byadhesive 135, for example. In this embodiment, stiffeners 139 areattached to CSP 114 with adhesive 135. CSP contacts 124, regardless ofconfiguration, generally will define a mounting height for CSP, such asmounting height H depicted in FIG. 23A for CSP contacts comprisingsolder balls. Preferably, thickness T of stiffeners 139 is less thanmounting height H, for example as depicted in FIG. 23A, with thecombined thickness of stiffener 139 and adhesives 134 and 135approximately equal mounting height H so as to dispose the lower portionof the flex circuit 130 approximately parallel to the lower surface 118of CSP 114. In preferred embodiments, stiffeners 139 also are configuredto provide lateral clearance for the CSP arrays 126 comprising variousCSP contacts 124. In the exemplar depicted in FIG. 23, for example, CSPcontacts 124 are at least partially disposed within the volume 140between stiffeners 139.

Stiffeners 139 may take several useful configurations, but in preferredembodiments herein, stiffeners 139 are substantially planar. A preferredembodiment is shown using stiffeners 139 disposed within the lateralextent L of CSP 114. Other embodiments may have stiffeners 139 disposedat least partially outside lateral extent L of CSP 114, one example ofwhich is the embodiments further discussed below in connection with FIG.38.

In preferred embodiments, flex circuit 130 has upper portions 130U thatterminate in edges 170A and 170B which are separated by gap G above theupper surface 116 of CSP 114. In some embodiments, gap G is preselectedand imposed when precursor assembly 105 is made. Upper portions 130U offlex circuit 130 are disposed along the upper surface 116 of CSP 114even if literally separated from that surface, such as by adhesive 171,for example. In such configurations, flex circuit 130 has a foldedportion 131.

FIG. 23 depicts precursor assembly 105 with module contacts 136 throughwhich the precursor assembly 105 may connect to an applicationenvironment or to another precursor assembly 105, for example, as shownin FIG. 34. In the illustrated embodiment, the module contacts 136 aredeployed in a module contact array 138, but other configurations ofmodule contacts may be used. Those of skill will recognize that modulecontacts 136 in the form of the depicted solder balls are not requiredto connect a stacked circuit module 110 to an application environment orto connect a precursor assembly 105 to another precursor assembly 105,and that other connective strategies may be employed such as, forexample, direct pad to pad connection schemes or connective structuresother than solder balls.

A preferred method for practicing the invention produces precursorassemblies 105 in batches of six. The stiffener(s) and flex circuit(s)for a particular precursor assembly are provided in aggregation withother stiffeners and flex circuits, respectively, for other precursorassemblies. Those of skill will recognize, however, that the inventivemethods described herein can be used with other batch sizes or withcontinuous production techniques, for example those using known reel andtape formats. FIG. 24 depicts an exemplar strip or panel of stiffenerstock 237 that may be employed in some preferred embodiments of thepresent invention, and FIG. 25 depicts an enlarged depiction of the areamarked “25” in FIG. 24. The illustrated strip of stiffener stock 237includes twelve stiffeners 139 retained by tabs 238 in configuration fordeployment in six precursor assemblies 105. The stiffener material hascutouts comprising tooling holes 239 and windows 240. Windows 240 areconfigured to accommodate CSP arrays 126 comprising CSP contacts 124 ofCSP 114. At each longitudinal end of the stiffener stock 237 depicted,tabs 238A and tooling holes 239A are disposed generally as half of a tab238 and a tooling hole 239 as disposed between adjacent windows 240.

Stiffener stock 237 as depicted in the embodiment of FIG. 24 comprises apolymer having thermal properties adequate for the various temperaturesat which various solder reflow and other attachment operations may occurin the production of precursor assemblies 105 and stacked circuitmodules 110 and in the deployment of stacked circuit modules 110 in anapplication environment. In a preferred embodiment, stiffener stock 237comprises a single layer or multiple laminated layers of polyimide filmselected so that stiffeners 139 have mechanical properties compatiblewith the mechanical properties of flex circuit 130, but other materialsthat are compatible with the assembly processes may be used such asresin polymer matrix composites, engineering ceramics or ceramic fibers,graphite composites, or filled and non-filled plastics known to those ofskill in the art. Preferably, compatibility of the mechanical propertiesof stiffeners 139 and flex circuit 130 are selected to reduce to anacceptable extent any warping and other deformations of precursorassembly 105 caused by differential thermal expansion of stiffeners 139and flex circuit 130. As those of skill will recognize, stiffener stock237 also may take other configurations and compositions and may, forexample, be devised in more than one piece and/or be devised of materialthat is thermally conductive. In alternative embodiments, stiffenerstock 237 may comprise material of sufficient rigidity such as stainlesssteels, aluminum, copper, or other metals or metal alloys so thatstiffeners 139 control the coplanarity of CSP 114 by inhibiting warping.

FIGS. 26 and 27 depict perspective and plan views, respectively, ofstiffener stock 237 disposed on a panel or strip 230 comprising flexcircuits 130. In the depicted embodiment, six flex circuits 130 areconfigured side-by-side, with a portion of each flex circuit 130accessible through a respective window 240 of stiffener stock 237. Strip230 further comprises lateral edges 231 and strip edge portions 232. Ina preferred embodiment, an adhesive 134 (shown earlier) is used toattach stiffener stock 237 and its component stiffeners 139 and tabs 238to strip or panel 230 and its component flex circuits 130. Adhesive 134in a preferred embodiment comprises a dry film adhesive. Those of skillwill recognize, however, that adhesive 134 may be selectively applied toselected portions of stiffener stock 237 or strip 230, or both, and thatother methods for attaching stiffeners 139 to flex circuits 130 may beemployed in accordance with various embodiments of the present inventionincluding, for example, laminate tape adhesive, liquid adhesive, andultrasonic or thermal bonding. Preferably, the adhesive will bethermally conductive. In a preferred embodiment, tooling holes 239facilitate alignment of stiffener stock 237 and strip 230, althoughalternative methods such as machine vision aided pick & place may beemployed.

FIG. 28 depicts an enlarged depiction of the area marked “28” in FIG.27. The depiction of FIG. 28 is centered on a site where a CSP 114 willbe disposed. When a CSP 114 is disposed, selected CSP contacts 124 willbe connected to respective ones of flex contacts disposed in flexcontact arrays. For simplicity, the depiction of FIG. 28 shows throughwindow 240 only selected ones of flex contacts 144 of a selected flexcontact array 146. Components of stiffener stock 237 relevant to theillustrated site include stiffeners 139, tabs 238, tooling holes 239,and window 240.

The portion of strip 230 depicted in FIG. 28 also illustrates variousfeatures of flex circuit 130 of a preferred embodiment. In theillustrated embodiment, a singulation opening 233 is disposed throughstrip 230 adjacent to each longitudinal end of each stiffener 139.Additional singulation openings 234 are disposed through strip 230 alongstrip edge portions 232 adjacent to each lateral edge 231 of strip 230.Edges 170A and 170B of upper portions 130U of flex circuit 130 aredisposed along singulation openings 234, with each upper portion 130Udisposed between a respective singulation opening 234 and a respectivestiffener 139.

Strip 230 and the flex circuits 130 disposed thereon can be configuredwith conductive components in a wide variety of ways. For example, strip230 and the flex circuits 130 disposed thereon can be multi-layerflexible circuit structures, such as the embodiment discussed abovehaving a first conductive layer and a second conductive layer that areinterior to first and second outer surfaces, with an intermediate layerdisposed between the first conductive layer and the second conductivelayer. As those of skill in the art will recognize, a single conductivelayer or three or more conductive layers can also be used, and typicallythe choice will depend on the complexity of the circuit routingrequired. Further, some embodiments may employ only one cover coat, suchas those instances in which a ground plane is exposed. Circuit tracescan be disposed in one or more conductive layers, and selectedconductive layers may contain only ground or voltage planes.

In one exemplar preferred embodiment useful for stacking memory CSPs,conductive traces are disposed at one conductive layer with a groundplane disposed an another conductive layer. In that embodiment, a singleouter surface is used leaving one of the conductive layers exposed. Allcontact pads on the exposed conductive layer are connected to the otherconductive surface through vias, using no conductive traces on theexposed conductive layer. Connecting the contact pads directly throughvias mitigates solder wicking and reduces costs and thickness of theflex circuitry.

The manufacture of strip 230 may employ various electroplating stepsthat use current supplied from sprocket rails engaging sprocket holes235. Current for electroplating can be routed along bussing through trimtabs 250, which are severed from flex circuits 130 during singulation asdiscussed further below. Electroplating bus paths also can converge atvarious connection points of strip 230, which bussing connections can besevered following electroplating by making de-bussing punches 251 asillustrated in FIG. 28. As those of skill in the art will recognize,however, other methods may be used to dispose conductive material withinand/or on strip 230. At each longitudinal end of flex circuit 130 in apreferred embodiment, nonbussed portion 150 of flex circuit 130 isdisposed alongside tab 238 and between singulation openings 233 toprovide additional clearance for circuitry of flex circuit 130 duringsingulation, as discussed further below.

FIG. 28 also depicts the various pattern recognition marks, or“fiducials,” used by automated assembly equipment during manufacture ofprecursor assemblies 105. Preferably, fiducials are metal defined,asymmetrically placed, and comprise a cross and a square wherepractical. The preferred embodiment depicted has global fiducials 260defined by circular metal regions on the surface of strip 230 andaligned with tooling holes 239. Additional global fiducials are definedby metal regions in the form of a square (fiducials 261) and a cross(fiducials 262). The global fiducials are used as reference pointsduring singulation of precursor assemblies 105 or stacked circuitmodules 110. Also depicted are local fiducials defined by metal regionsin the form of a square (fiducials 161) and a cross (fiducials 162)defined in a conductive layer of the flex circuit, which local fiducialsare used by automated equipment as a reference during the placement ofCSP 114 on flex circuit 130.

Although the description of the embodiment illustrated in FIG. 28 isdirected to features related to a single precursor assembly 105 to bemade using stiffener stock 237 and strip 230, those of skill willrecognize that the described features can be replicated for otherprecursor assemblies 105 or that variations in the described featurescan be employed for other precursor assemblies 105.

Prior to placement of CSP 114 on flex circuit 130, in the disclosedembodiment adhesive 135 is applied to the exposed upper surface ofstiffener 139. In a preferred embodiment, adhesive 135 comprises aliquid adhesive. Those of skill will recognize, however, that adhesive135 may be selectively applied to selected portions of stiffener 139 andthat other methods for attaching stiffeners 139 to CSP 114 may beemployed in various embodiments of the present invention including, forexample, laminate tape adhesive and dry film adhesive. Preferably, theadhesive will be thermally conductive.

Automated pick-and-place equipment know in the art is used to disposeCSP 114 on flex circuit 130 in a preferred embodiment. Thepick-and-place equipment dips CSP contacts 124 in flux prior toplacement of CSP 114 on flex circuit 130. After placement of CSP 114 onflex circuit 130, heat is supplied during a first solder reflowoperation to produce a solder connection between CSP contacts 124 andflex contacts 144. The combination of adhesive 134, stiffener 139, andadhesive 135 cooperate to maintain flex circuit 130 and CSP 114 inproper position during the first solder reflow operation.

After CSP 114 is soldered to flex circuit 130, upper portions 130U offlex circuits 130 are separated from strip 230 by upper flex cuts 174.FIG. 29 depicts the position of upper flex cuts 174, and also shows theposition of singulation cuts 175 made later during singulation ofprecursor assemblies 105 or stacked circuit modules 110 as discussedbelow. FIG. 30 depicts the configuration of flex circuit 130, stiffeners139, and CSP 114 following the making of upper flex cuts 174 as shown inFIG. 29, with such depiction bounded to the left and right by thepositions where singulation cuts 175 will be made later in the assemblyprocess.

In the depicted embodiments, adhesive 171 is applied to the uppersurface 116 of CSP 114, to upper portions 130U of flex circuit 130, orto both upper surface 116 and upper portions 130U. In a preferredembodiment, adhesive 171 comprises a dry film adhesive. Those of skillwill recognize, however, that adhesive 171 may be selectively applied toselected portions of upper surface 116 or upper portions 130U, or both,and that other methods for attaching the upper surfaces 118 to flexcircuits 130 may be employed in various embodiments of the presentinvention including, for example, laminate tape adhesive and liquidadhesive. Preferably, the adhesive will be thermally conductive.

As shown in FIGS. 23 and 31, in the disclosed embodiments, upperportions 130U of flex circuit 130 are disposed along the upper surface116 of CSP 114 even if literally separated from that surface, such as byadhesive 171, for example. Disposition of upper portions 130U of flexcircuit 130 along the upper surface 116 of CSP 114 can be accomplishedusing a tooling apparatus 180 devised in accordance with a preferredembodiment of the present invention, as depicted in FIGS. 39-43 anddiscussed below. FIG. 31 depicts flex circuit edges 170A and 170B in aproximal arrangement according to a preferred embodiment of the presentinvention.

As exemplified by the embodiment illustrated in FIG. 31, flex circuit130 is configured for external electrical connection of lower CSP 114.Referring to FIG. 31, upper sides 133 of upper portions 130U of flexcircuit 130 are depicted having upper flex contacts or pads 142 disposedin a first upper flex contact array 148A and a second upper flexcontract array 148B. As those of skill will recognize, first upper flexcontact array 148A and second upper flex contract array 148B have beenabstracted to illustrate an exemplar set of upper flex contacts 142 whenin practice, first upper flex contact array 148A and second upper flexcontract array 148B may include a greater or lesser number of individualupper flex contacts or have flex contacts disposed in a differentconfiguration, or both.

The depiction of FIG. 31 shows flex edges 170A and 170B separated by gapG. Flex edges 170A and 170B terminate respective upper portions 130U offlex circuit 130. Whether one or two distinct flex circuits areemployed, gap G between edges 170A and 170B is controlled by a physicalform during assembly of precursor assembly 105 and first upper flexcontact array 148A and second upper flex contract array 148B will,therefore, be localized or fixed in relative position. In the exemplaryembodiments, first upper flex contact array 148A and second upper flexcontract array 148B together define an array of upper flex contacts 142configured for connection to CSP contacts 124 of upper CSP 112.

Other means may be employed to position or set edges 170A and 170B and,by extension, first upper flex contact array 148A and second upper flexcontract array 148B. For example, flex edges 170A and 170B may bedevised to be jointly fittable with each other as shown in FIG. 32 toposition first upper flex contact array 148A and second upper flexcontract array 148B. Protrusion 176 fits with receptive check 177 toboth align laterally and transversely edges 170A and 170B. Other similardevices may be employed to laterally and/or transversely align edges170A and 170B. Thus, first upper flex contact array 148A and secondupper flex contract array 148B are disposed in predetermined relation toeach other by the jointly fittable configuration of edges 170A and 170Bto mesh with each other. Consequently, in this depicted alternativeembodiment, edges 170A and 170B are disposed in predetermined relationto each other by their jointly fittable configurations.

Stacked circuit modules devised in accordance with the invention cancomprise multiple precursor assemblies 105 as shown in FIG. 34 or asingle precursor assembly 105 as shown in FIG. 35. When assemblingprecursor assemblies 105 for use in stacked circuit modules comprisingmultiple precursor assemblies 105, the precursor assemblies 105 can besingulated at this stage with singulation cuts 175, placed for exampleas depicted in FIG. 29. In such embodiments, module contacts 136 aredisposed along flex contacts or pads 149 on flex circuit 130 asexemplified in FIG. 33, which depicts a plan view of an exemplarprecursor assembly 105 from below. As those of skill will recognize,module contact arrays 138 have been abstracted to illustrate an exemplarset of module contacts 136 when in practice, module contact arrays 138may include a greater or lesser number of individual module contacts ormodule contacts disposed in a different configuration. Alternatively, inpreferred embodiments singulation with singulation cuts 175 can bedeferred until all precursor assemblies 105 and upper CSPs 112 have beenassembled.

FIG. 34 depicts an exemplar stacked circuit module 110 in accordancewith a preferred embodiment of the present invention that employs threeprecursor assemblies 105. In this embodiment, each flex circuit 130 hasfolded portions 131 respective disposed adjacent to first and secondlateral sides of the stack. As those of skill in the art will recognize,however, stacked circuit modules 110 also can be devised with one, two,three, four, or more precursor assemblies 105, or with precursorassemblies using CSPs of different types. In some configurations, one ormore lower CSPs 114 may have a lateral extent L having a proportion suchthat folded portions 131 of one or more other precursor assemblies 105may not be disposed outside such lateral extent.

FIG. 35 depicts an exemplar stacked circuit module 110 in accordancewith a preferred embodiment of the present invention that employs asingle precursor assembly 105. In this embodiment, flex circuit 130 hasfolded portions 131 respective disposed adjacent to first and secondlateral sides of the stack. For stacked circuit modules 110 comprisingone lower CSP 114, in a preferred embodiment upper CSP 112 is attachedto flex circuit 130 prior to singulation of stacked circuit modules 110.Automated pick-and-place equipment know in the art is used to disposeupper CSP 112 on flex circuit 130 as shown in FIG. 35. Thepick-and-place equipment dips CSP contacts 124 in flux prior toplacement of CSP 112 on flex circuit 130. After placement of CSP 112 onflex circuit 130, the stacked circuit modules 110 are clamped while heatis supplied during a second solder reflow operation to produce a solderconnection between CSP contacts 124 and upper flex contacts 142. Thecombination of adhesive 134, stiffener 139, adhesive 135, and adhesive171 cooperate to maintain flex circuit 130 and CSP 114 in properposition during the second solder reflow operation.

In a preferred embodiment, module contacts 136 are disposed along flexcontacts or pads 149 on flex circuit 130 in module contact arrays 138.FIGS. 36 and 37 depict, respectively, lower perspective and upperperspective views of an exemplar stacked circuit module 110 inaccordance with a preferred embodiment of the present invention thatemploys a single precursor assembly 105. Exemplar stacked circuitmodules 110 typically are connected to an application environment, suchas a printed circuit board, in a third solder reflow operation. Thecombination of adhesive 134, stiffener 139, adhesive 135, and adhesive171 cooperate to maintain flex circuit 130, CSP 114, and CSP 112 inproper position during the third solder reflow operation.

FIG. 38 depicts an exemplar stacked circuit module 110 in accordancewith a preferred embodiment of the present invention that has stiffeners139 disposed at least partially outside lateral extent L of CSP 114.Embodiments as illustrated in FIG. 38 may be devised when using a strip230 and stiffener stock 237 devised for use with a CSPs having largerdimensions than CSP 114 depicted in FIG. 38. Accordingly, in preferredembodiments, a single size of strip 230 and stiffener stock 237 can beused for a variety of CSP package sizes. In various embodiments ofprecursor assembly 105 in which stiffeners 139 are disposed at leastpartially outside lateral extent L of CSP 114, the portions ofstiffeners 139 outside lateral extent L will substantially control thesize of gap G in many alternative methods of assembly.

A wide variety of other variations in the configuration and materials ofprecursor assemblies 105 and stacked circuit modules 110 will beapparent to those skilled in the art. For example, tabs 238 need not berectangular or completely trimmed away during singulation withsingulation cuts 175, but can also extend along some or all of the endsof precursor assembly 105. Singulation openings 233 and upper flex cuts174 can take other shapes and be disposed in different positions, whichfor example provide a narrower portion of flex circuit 130 betweenstiffener 139 and upper surface 116 of CSP 114 to allow enhancedventilation. In alternative embodiments, a stabilizing fill may beemployed between flex circuit 130 and CSP 114, for example asillustrated by conformal media 40 depicted in FIGS. 2 and 16.

In preferred embodiments, a low profile for precursor assembly 105 isprovided. In such embodiments, stiffener 139 typically is about 0.13 mmthick, and adhesive 134 is about 0.05 mm thick. Adhesive 135 typicallyis about 0.07 mm thick, but can range across a variety of thicknesses.For example, in various preferred embodiments Adhesive 135 ranges fromabout 0.04 mm. to about 0.10 mm thick. Adhesive 171 typically is about0.08 mm thick. The various thicknesses used in embodiments devised inaccordance with the invention are subject to wide ranges ofalternatives, as those of skill will recognize.

FIG. 39 depicts a tooling apparatus 180 devised in accordance with apreferred embodiment of the present invention illustrating the use of aphysical form to set gap G between edges 170A and 170B of flex circuit130. Tooling apparatus 180 includes a flex aligner 182 as shown in FIG.39 used as a physical form to impose a preselected distance between thefirst and second edges. When forming tool 184 disposes flex circuit 130adjacent to upper surface 116 of CSP 114 in forming precursor assembly105, edges 170A and 170B of flex circuit 130 are limited in lateralplacement along upper surface 116 of CSP 114 by flex aligner 182. Gap“G” is, therefore, preselected and determined by the dimensions of flexaligner 182 when disposed between edges 170A and 170B. With gap G andedges 170A and 170B thus determined, first upper flex contact array 148Aand second upper flex contract array 148B are positioned during assemblyas exemplified in FIG. 31.

FIG. 40 depicts an enlarged depiction of the area marked “40” in FIG.39. As shown in the construction of the example precursor assembly 105,flex circuit 130 is attached to stiffener 139 with adhesive 134. Whenprecursor assembly 105 comprising CSP 114, stiffeners 139, adhesives 134and 135, and flex circuit 130 is disposed in cavity 188 of jig 186, flexcircuit 130 is deflected in an upward direction as shown in FIG. 40.

FIG. 41 illustrates a step in a method of devising an precursor assembly105 in accordance with a preferred embodiment of the present invention.As indicated, forming tools 184 are moveable as indicated by the arrow184M to indicate with the “+” sign movement of forming tools 184 todispose upper ends 130U of flex circuit 130 over CSP 114. The ends 170Aand 170B are set apart at distance “G” apart by flex aligner 182.

FIG. 42 illustrates another step in a method for devising a precursorassembly 105 in accordance with a preferred embodiment of the presentinvention. Press tool 189 is imposed on precursor assembly 105 afterupper portions 130U of flex circuit 130 have been disposed over theupper surface 116 of the CSP 114 and forming tools 184 are withdrawn asindicated by the arrow 184M to indicate with the “−” sign movement offorming tools 184. Press tool 189 preferably may be heated.

FIG. 43 depicts another step in a method for devising a precursorassembly 105 in accordance with a preferred embodiment of the presentinvention. Press tool 189 has moved up off of precursor assembly 105 asindicated by motion arrow 189M. Flex aligner 182 may now be withdrawnand precursor assembly 105 is ready for combination with either anotherprecursor assembly 105 or a CSP 112 to form a module 110.

FIG. 44 depicts a tooling apparatus 180 devised in accordance withanother preferred embodiment of the present invention also using aphysical form to set gap G between edges 170A and 170B of flex circuit130. In a step of a preferred method for using the tooling apparatus 180depicted in FIG. 44, jigs 186 are placed in first configuration withjigs 186 set apart by a first width W1. In this embodiment, precursorassembly 105 comprising CSP 114, stiffeners 139, adhesives 134 and 135,and flex circuit 130 is disposed in cavity 188 by flex aligner 182, andupper portions 130U of flex circuit 130 are deflected in an upwarddirection in the configuration shown in FIG. 44 by preform tools 187comprised in press tool 189A.

In the embodiment depicted in FIG. 45, press tool 189A used for the stepdepicted in FIG. 44 is retracted and exchanged for press tool 189Bshown, which does not comprise preform tools 187. With precursorassembly 105 raised above cavity 188, jigs 186 are moved in thedirection indicated by motion arrows 186M to a second configuration, inwhich jigs 186 are set apart by a second width W2. In the configurationdepicted in FIG. 45, the flex preformed by the step depicted in FIG. 44relaxes, with upper portions 130U of flex circuit 130 springing back tosome extent from the position depicted in FIG. 44.

FIG. 46 depicts another step in a preferred method for using theillustrated tooling apparatus 180. With jigs 186 set apart by secondwidth W2, precursor assembly 105 is disposed in cavity 188 by flexaligner 182, which causes upper portions 130U of flex circuit 130 to bedeflected in an inward direction in the configuration shown in FIG. 46by interference with jigs 186 set apart at second width W2.

FIG. 47 depicts another step in a preferred method for using theillustrated tooling apparatus 180. With upper portions 130U of flexcircuit 130 disposed above CSP 114, such as depicted in FIG. 46, presstool 189B is imposed on precursor assembly 105. Press tool 189Bpreferably may be heated. In this configuration, the ends 170A and 170Bof flex circuit 130 are set apart at distance G by flex aligner 182, andupper portions 130U of flex circuit 130 are attached to top surface 116of CSP 114 by adhesive 171, for example as illustrated in FIG. 23.

FIG. 48 depicts another step in a method for devising a precursorassembly 105 in accordance with a preferred embodiment of the presentinvention. Press tool 189B has moved up off of precursor assembly 105 asindicated by motion arrow 189M. Flex aligner 182 may now be withdrawnand precursor assembly 105 is ready for combination with either anotherprecursor assembly 105 or a CSP 112 to form a module 110.

The tooling apparatus and methods depicted in FIGS. 44-48 do not have oruse forming tools 184 such as those depicted in FIGS. 39-43, but formingtools 184 and other similar structures could be used in the methods andwith the tooling apparatus depicted in FIGS. 44-48 instead of, or with,press tool 189B.

Although the present invention has been described in detail, it will beapparent to those skilled in the art that the invention may be embodiedin a variety of specific forms and that various changes, substitutionsand alterations can be made without departing from the spirit and scopeof the invention. The described embodiments are only illustrative andnot restrictive, and therefore the scope of the invention is indicatedby the following claims.

1. An assembly devised as a component for a stacked circuit module comprising: a first CSP comprising a package body having upper and lower major surfaces and first and second lateral sides, a lateral extent defined by the first and second lateral sides, first CSP contacts disposed along the lower major surface, and a mounting height defined by the first CSP contacts; a flex circuit configured for external electrical connection of the first CSP, the flex circuit comprising lower flex contacts connected to selected ones of the first CSP contacts, and first and second upper portions terminated by first and second edges, respectively, the first and second upper portions of the flex circuit being disposed above the upper major surface of the first CSP, and the first and second edges being disposed a preselected distance apart within the lateral extent defined by the first and second lateral sides; and first and second generally planar stiffeners each attached to the lower major surface of the first CSP and each having a thickness that does not exceed the mounting height, the first generally planar stiffener being disposed along the first lateral side of the first CSP and the second generally planar stiffener being disposed along the second lateral side of the first CSP.
 2. The assembly of claim 1 in which the flex circuit has plural conductive layers.
 3. The assembly of claim 1 in which the first and second generally planar stiffeners are disposed within the lateral extent defined by the first and second lateral sides.
 4. The assembly of claim 1 in which portions of the first and second generally planar stiffeners are disposed outside the lateral extent defined by the first and second lateral sides.
 5. The assembly of claim 1 in which the first and second generally planar stiffeners are attached to the flex circuit with adhesive.
 6. The assembly of claim 5 in which the adhesive is a dry film adhesive.
 7. The assembly of claim 1 in which the first and second generally planar stiffeners are attached to the first CSP with adhesive.
 8. The assembly of claim 7 in which the adhesive is a liquid adhesive.
 9. The assembly of claim 1 in which the first CSP contacts at least partially project into a volume between the first and second generally planar stiffeners.
 10. The assembly of claim 1 in which the first upper portion exhibits first upper flex contacts and the second upper portion exhibits second upper flex contacts, the first and second upper flex contacts being collectively configured for connection to a second CSP.
 11. The assembly of claim 1 in which the first and second generally planar stiffeners comprise one or more laminated layers of polyimide film having mechanical properties compatible with the mechanical properties of the flexible circuit.
 12. The assembly of claim 9 in which the first and second generally planar stiffeners comprise one or more laminated layers of polyimide film having mechanical properties compatible with the mechanical properties of the flexible circuit.
 13. The assembly of claim 3 or 4 in which: the first and second generally planar stiffeners are attached to the flex circuit with adhesive; the first and second generally planar stiffeners are attached to the first CSP with adhesive; the first CSP contacts at least partially project into a volume between the first and second generally planar stiffeners; the first upper portion exhibits first upper flex contacts and the second upper portion exhibits second upper flex contacts, the first and second upper flex contacts being collectively configured for connection to a second CSP; and the first and second generally planar stiffeners comprise one or more laminated layers of polyimide film having mechanical properties compatible with the mechanical properties of the flexible circuit.
 14. A stacked circuit module comprising: an assembly devised according to claim 1; and a second CSP disposed above the assembly and connected to the flex circuit.
 15. A stacked circuit module comprising: an assembly devised according to claim 13; and a second CSP connected to the flex circuit.
 16. An assembly devised as a component for a stacked circuit module comprising: a first CSP having upper and lower major surfaces, first and second lateral sides, and first CSP contacts disposed along the lower major surface; a flex circuit configured for external electrical connection of the first CSP, the flex circuit comprising lower flex contacts connected to selected ones of the first CSP contacts, and first and second upper portions terminated by first and second edges, respectively, the first upper portion of the flex circuit being disposed above the upper major surface of the first CSP along the first lateral side, the second upper portion of the flex circuit being disposed above the upper major surface of the first CSP along the second lateral side, and the first and second edges being disposed a preselected distance apart above the first CSP; a stiffener attached to the lower major surface of the first CSP.
 17. The assembly of claim 16 in which the first CSP contacts at least partially project below the lower major surface of the first CSP.
 18. The assembly of claim 16 in which the stiffener disposes the lower flex contacts apart from the lower major surface of the first CSP.
 19. The assembly of claim 18 in which the flex circuit has plural conductive layers.
 20. A high-density circuit module comprising: a stack comprising first and second lateral sides, a first CSP having a first major surface along which a first plurality of CSP contacts is disposed and a second major surface, and a second CSP having a major surface along which a second plurality of CSP contacts is disposed; a flex circuit having at least one outer layer, a first generally planar portion disposed adjacent to at least a portion of the first major surface of the first CSP, a second generally planar portion disposed adjacent to at least a portion of the second major surface of the first CSP, and a folded portion disposed adjacent to first lateral side of the stack; sets of flex contacts, respectively comprising a first plurality of flex contacts along a first side of the first generally planar portion of the flex circuit, a second plurality of flex contacts along the second generally planar portion of the flex circuit, and a third plurality of flex contacts disposed along a second side of the first generally planar portion of the flex circuit; a plurality of module contacts; conductive connections between ones of the first plurality of CSP contacts and ones of the first plurality of flex contacts; conductive connections between ones of the second plurality of CSP contacts and ones of the second plurality of flex contacts; and conductive connections between ones of the plurality of module contacts and ones of the third plurality of flex contacts.
 21. The high-density circuit module of claim 20 in which the flex circuit comprises a plurality of conductive layers, and a first of the conductive levels comprises a ground plane.
 22. The high-density circuit module of claim 21 in which a second of the conductive levels has plural electrical paths, each between a selected one of the contacts of the first plurality of CSP contacts and a selected one of the contacts of the second plurality of CSP contacts.
 23. The high-density circuit module of claim 22 in which the second conductive layer comprises a voltage plane, and the electrical paths comprise traces.
 24. The high-density circuit module of claim 22 in which selected ones of the electrical paths have substantially equal signal lengths.
 25. The high-density circuit module of claim 24 in which the second conductive layer comprises a voltage plane, and the electrical paths comprise traces.
 26. The high-density circuit module of claim 20 in which the flex circuit further comprises a third generally planar portion disposed adjacent to at least a portion of the second major surface of the first CSP, and a folded portion disposed adjacent to second lateral side of the stack.
 27. The high-density circuit module of claim 20 or 25 in which the flex circuit is attached to a stiffener disposed along the first major surface of the first CSP.
 28. The high-density circuit module of claim 20 in which the flex circuit is attached to a stiffener disposed along the first major surface of the first CSP, the stiffener disposing the first plurality of flex contacts apart from the first major surface of the first CSP but in contact with the first plurality of CSP contacts.
 29. An assembly devised as a component for a stacked circuit module comprising: a first CSP comprising upper and lower major surfaces and first CSP contacts disposed along the lower major surface; a flex circuit comprising plural conductive layers, lower flex contacts, and a first upper portion disposed above the upper major surface of the first CSP; and a stiffener attached to the lower major surface of the first CSP and to the flex circuit.
 30. The assembly of claim 29 in which the stiffener is configured to dispose the lower flex contacts of the flex circuit below the lower major surface of the first CSP.
 31. The assembly of claim 30 in which the first CSP contacts emerge from the lower major surface of the first CSP and contact the lower flex contacts below the lower major surface of the first CSP.
 32. The assembly of claim 29 in which the stiffener is disposed within a lateral extent defined by first and second lateral sides of the first CSP.
 33. The assembly of claim 29 in which a portion of the stiffener is disposed outside a lateral extent defined by first and second lateral sides of the first CSP.
 34. The assembly of claim 29 in which the stiffener is attached to the flex circuit with adhesive.
 35. The assembly of claim 34 in which the adhesive is a dry film adhesive.
 36. The assembly of claim 29 in which the stiffener is attached to the first CSP with adhesive.
 37. The assembly of claim 36 in which the adhesive is a liquid adhesive.
 38. The assembly of claim 29 in which the first upper portion of the flex circuit exhibits upper flex contacts configured for connection to a second CSP.
 39. The assembly of claim 29 further comprising first upper flex contacts along the first upper portion of the flex circuit and second upper flex contacts along a second upper portion of the flex circuit, the first upper flex contacts and second upper flex contracts collectively configured for connection to a second CSP.
 40. The assembly of claim 29 in which the stiffener comprises one or more laminated layers of polyimide film having mechanical properties compatible with the mechanical properties of the flexible circuit.
 41. The assembly of claim 29 in which the flex circuit comprises a first fiducial defined by a generally square metallic region and a second fiducial defined by a cross-shaped metallic region, the first and second fiducials being asymmetrically disposed along the flex circuit.
 42. The assembly of claim 40 in which the stiffener is about 0.13 mm thick the stiffener is attached to the flex circuit with a dry film adhesive about 0.05 mm thick; the stiffeners is attached to the first CSP with liquid adhesive between about 0.04 mm. to 0.10 mm thick; and the first upper portion of the flex circuit is attached to the upper major surface of the first CSP with a dry film adhesive about 0.08 mm thick.
 43. A method for constructing an assembly devised for employment in a stacked circuit module, the method comprising the steps of: providing a first CSP comprising upper and lower major surfaces and first CSP contacts disposed along the lower major surface; providing a flex circuit comprising lower flex contacts, and first and second upper portions terminated by first and second edges, respectively; providing a stiffener; attaching the stiffener to the flex circuitry; attaching the stiffener to the lower major surface of the first CSP; disposing the first and second upper portions of the flex circuitry above the upper major surface of the first CSP; and imposing a preselected distance between the first and second edges.
 44. The method of claim 43 in which a physical form is used to impose a preselected distance between the first and second edges.
 45. The method of claim 44 in which a portion of the physical form is placed between the first and second edges.
 46. The method of claim 43 in which the flex circuit comprises a fiducial, the method further comprising the steps of referring the fiducial and disposing the first CSP along the flex circuit.
 47. The method of claim 43 in which the stiffener is provided in a first aggregation having other stiffeners and the flex circuit is provided in a second aggregation having other flex circuits, the method further comprising the steps of referring to a fiducial comprised in the second aggregation and singulating the assembly from the first and second aggregations.
 48. The method of claim 47 in which the second aggregation comprises a trim tab having conductive bussing, the flex circuit of the assembly has an end portion having no conductive bussing, and the step of singulating comprises the steps of separating the trim tab from the flex circuit of the assembly and separating end portion of the flex circuit of the assembly from the second aggregation.
 49. A method for constructing a stacked circuit module, the method comprising the steps of: constructing an assembly devised for employment in a stacked circuit module in accordance with claim 43; providing a second CSP; and disposing the second CSP above the assembly and connecting the second CSP to the flex circuit.
 50. A tooling apparatus for constructing an assembly devised for employment in a stacked circuit module, the tooling apparatus comprising: a jig; a cavity configured to receive a CSP and a flex circuit; and a forming tool configured to dispose upper portions of a flex circuit received in the cavity along an upper surface of a CSP received in the cavity.
 51. The tooling apparatus of claim 50 further comprising a physical form configured to impose a preselected distance between a first edge and a second edge of a flex circuit received in the cavity.
 52. The tooling apparatus of claim 51 further comprising a press tool configured to impose portions of a flex circuit received in the cavity on an upper surface of a CSP received in the cavity.
 53. The tooling apparatus of claim 52 in which the press tool is heated.
 54. A method for constructing an assembly devised for employment in a stacked circuit module, the method comprising the steps of: providing a tooling apparatus in accordance with claim 50; disposing a CSP, a stiffener, and a flex circuit in the cavity of the tooling apparatus to deflect a first upper portion and a second upper portion of the flex circuit upward; and disposing the first and second upper portions of the flex circuit along an upper surface of the CSP with the forming tool.
 55. The method for constructing an assembly of claim 54 in which the tooling apparatus further comprises a physical form, the method further comprising the step of using the physical form to impose a preselected distance between a first edge and a second edge of the flex circuit.
 56. The method for constructing an assembly of claim 55 in which the tooling apparatus further comprises a press tool, the method further comprising the step of using the press tool to impose the first and second upper portions of the flex circuit on an upper surface of the CSP.
 57. The method for constructing an assembly of claim 56, the method further comprising the step of heating the press tool.
 58. A tooling apparatus for constructing an assembly devised for employment in a stacked circuit module, the tooling apparatus comprising: an adjustable jig; a preform tool; and a cavity configured to receive a CSP and a flex circuit, the cavity being defined at least in part by the adjustable jig.
 59. The tooling apparatus of claim 58 further comprising a physical form configured to impose a preselected distance between a first edge and a second edge of a flex circuit received in the cavity.
 60. The tooling apparatus of claim 59 further comprising a press tool configured to impose portions of a flex circuit received in the cavity on an upper surface of a CSP received in the cavity.
 61. The tooling apparatus of claim 60 in which the press tool is heated.
 62. The tooling apparatus of claim 61 further comprising a forming tool.
 63. A method for constructing an assembly devised for employment in a stacked circuit module, the method comprising the steps of: providing a tooling apparatus in accordance with claim 58; adjusting the jig to a first configuration; disposing a CSP, a stiffener, and a flex circuit in the cavity of the tooling apparatus using the preform tool to deflect a first upper portion and a second upper portion of the flex circuit upward to a first flex configuration; adjusting the jig to a second configuration; and disposing the CSP, the stiffener, and the flex circuit in the cavity of the tooling apparatus to deflect the first upper portion and the second upper portion of the flex circuit upward to a second flex configuration.
 64. The method for constructing an assembly of claim 63 in which the tooling apparatus further comprises a physical form, the method further comprising the step of using the physical form to impose a preselected distance between a first edge and a second edge of the flex circuit.
 65. The method for constructing an assembly of claim 64 in which the tooling apparatus further comprises a press tool, the method further comprising the step of using the press tool to impose the first and second upper portions of the flex circuit on an upper surface of the CSP.
 66. The method for constructing an assembly of claim 65, the method further comprising the step of heating the press tool.
 67. The method for constructing an assembly of claim 65 in which the tooling apparatus further comprises a forming tool, the method further comprising the step of disposing the first and second upper portions of the flex circuit along an upper surface of the CSP with the forming tool. 